The present invention concerns articles comprising a polypropylene nonwoven fabric (NWF) bonded with a polyolefin film, and the process for their preparation.
Articles consisting of a thin nonwoven fabric bonded with polyolefin film are well known and commercially available and are found in a number of applications, for example coverstock for sanitary napkins, gowns and protective clothing for the medical sector, disposable tablecloths and sheets. The material which forms the thin NWF is obtained from polypropylene fibers, cohered by passing them through a carding machine ("card web"), or thermosealed by way of calendering.
The films used for the production of the above mentioned articles consist of homo- and copolymers of ethylene, particularly low density polyethylene (LDPE), linear low density polyethylene (LLDPE), ethylene/vinyl acetate copolymers (EVA), high density polyethylene (HDPE), or a mixture of two or more of said polymers.
In order to achieve an effective bond between the two layers (NWF and film) by using the above mentioned materials, one needs to interface said layers with adhesives, such as hot melt, or solutions or emulsions of adhesive substances. These measures, however, present some inconveniences: they introduce solvent residues into the article (if one uses the above adhesive substances) which are undesirable for use in sanitary/hygienic applications; they cause the article to be more rigid, paper-like and noisy, where the desirable qualities are usually softness, flexibility and noiselessness.
A technically and economically attractive alternative would be the bonding of two layers by thermobonding, optionally using the thermosealing by points method. This type of sealing, however, is very difficult because of the different chemical nature of the two layers. Only by using high temperatures and long periods of time could one partially achieve said bonding (with poor results), by causing the partially melted film to penetrate the NWF; however, the article obtained with this method would be even more rigid and paper-like than the one produced by using the adhesives.